a girl who is somehow outside relationships
In fiction, the female is usually a factor in romantic or sexual relationships. They are either portrayed as being a "slut" and chasing after all the guys, or a "prude" and having to overcome this in order to find her true love. And then there's this girl. Like the Non-Action Guy, a girl who rather than being into relationships or actively averse to them, could not care less is somehow counter to what's expected of women. Since relationships are a two-way street, in order to fulfill this requirement, not only are they not interested in anyone romantically, but there doesn't seem to be anyone interested in them. Often a trait of the Emotionless Girl, although some of them can in fact become involved in relationships (somehow) despite their deadpan personality.